SetVarsFromFiles.cmake:

* tests!
* support a list variable expansion including expansion in a list value.
* fix variable declaration line number to the first line instead of the last
  line
* fix incorrect OS list variables declaration (UNIX while in WINDOWS and vice
  versa)
* better diagnostic for messages like:

    ```
    CMake Error at _externals/tacklelib/cmake/tacklelib/SetVarsFromFiles.cmake:2748 (message):
      ODR violation, variables must declare the same value:
      `.../_out/config/myproj/cmake/config.0.vars`(60): `top
      CMAKE_GENERATOR_PLATFORM` => [WIN:::X86] -> [WIN:MSVC14.16::X86]: `` ->
      `Win32` (is_path=`-1`)
    ```

    Needs to print both the next and the previous places of delaration.
    Currently only the next does print.

testlib:

* implement search for a test case function/macro directly in an inclusion file
  before include it to filter out test cases by a test case filter before
  run a cmake process with inclusion file.
  Leave the `tkl_testmodule_run_test_cases` function as an optional to
  explicitly declare test case list to enable/disable tests.

File.cmake

* remove `file` function override present as a workaround (may be not required
  anymore) to remove x16 slowdown.
